Vehicles have been developed to perform an idle-stop when idle-stop conditions are met and then automatically restart the engine when restart conditions are met. Such idle-stop systems enable fuel savings, reduction in exhaust emissions, reduction in noise, and the like.
Many factors may contribute to the engine automatically restarting without receiving any input from the operator. As one example, the engine may be automatically restarted when a vehicle battery state of charge (SOC) falls below a predetermined threshold, such as 30% SOC. In such a situation, the engine may be restarted, even though the brake pedal is engaged by the operator, for a sufficient amount of time to allow the battery parameter to be returned to the desired level (for example, to at least 30% SOC). Following a resetting of the parameter, the engine may return to the shutdown state.
However, the inventors have recognized several potential issues with such a method. As one example, during subsequent restarts, if the transmission remains coupled to the wheels, the operator may feel an uncomfortable feeling during engine restarts not initiated by an operator's launch request. However, if the transmission were decoupled from the wheels during a shutdown and no torque was provided to the wheels during subsequent restarts, when an operator subsequently requests a vehicle launch, a desirable fast launch may not be achievable.
Thus in one example, some of the above issues may be addressed by a method of controlling a powertrain of a vehicle, the powertrain including an engine and an automatic transmission, the powertrain coupled to driving wheels of the vehicle, and the vehicle operated by an operator. The method may comprise, selectively shutting down engine operation responsive to operating conditions and without receiving an engine shutdown request from the operator, and maintaining the automatic transmission in gear during the shutdown. The method may further comprise, during an engine restart from the shutdown condition, and with the transmission in gear, transmitting reduced torque to the transmission.
In one example, the operating conditions may include a high battery state of charge, or no request for cabin cooling. As such, during such operating conditions, and when no request for an engine shutdown is made by the operator, a first automatic engine shutdown may be performed. In another example, operator requested engine shutdown conditions may include an ignition key-off condition or an actuated engine shut-down button. As such, during such operator requested conditions, a second alternative engine shutdown may be performed. During either engine shutdown, the transmission may be kept in gear. Furthermore, during a subsequent engine restart from shutdown conditions, the transmission may be kept in gear so that a reduced torque may be transmitted to the automatic transmission. In one example, the reduced torque may be provided by actuating the transmission to internally lock the transmission and block transfer of input torque to the wheels. In another example, the decreased torque may be provided by increasing slippage of a forward clutch of the transmission. In still another example, a combination of transmission actuation and slippage increase may be employed, a relative amount of transmission actuation to slippage increase determined at least by engine operating conditions.
In another embodiment, the method comprises, selectively shutting down engine operation responsive to operating conditions and without receiving an engine shutdown request from the operator. The method further comprises, during a first engine restart from the shutdown condition, and with the transmission in gear, transmitting decreased torque through the transmission to launch the vehicle; and during a second engine restart from the shutdown condition, and with the transmission in gear, transmitting increased torque through the transmission.
In one example, a first or automatic restart (or non-launch based restart) may be performed responsive to restart conditions and without a launch request from the operator. Herein, a decreased torque may be transmitted through the transmission by increasing clutch slippage of a forward clutch of the transmission, by actuating the transmission to thereby internally lock the transmission and block transfer of input torque to the wheels, or a combination thereof. In another example, a second or launch-based restart may be performed responsive to restart conditions and with a launch request from the operator. Herein, an increased torque may be transmitted through the transmission by engaging a forward clutch of the transmission, reducing slippage of the forward clutch, engaging a torque converter lock-up clutch, reducing slippage of the torque converter lock-up clutch, or any combination thereof.
In this way, by maintaining the transmission in gear during the shutdown, as also during a subsequent engine restart, a fast vehicle launch may be provided when a restart is requested by the operator. By reducing the torque transmitted during an automatic engine restart, the drive-feel effect of the restart may be reduced. In this way, issues related to both launch-based restarts and automatic (or non-launch based) restarts may be addressed.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.